Suspension liners provide a soft, flexible interface between a residual limb of an amputee and a hard socket to which a prosthetic device is secured. These liners are typically made of an air impermeable elastomer material and may include a reinforcement layer intermediate the inner and outer surfaces of the liner body or externally thereof to provide resistance against axial elongation of the elastomer constituting the liner body. Such reinforcement typically does not restrict radial distension or stretching of the liner body.
The liners may also include an outer covering different from the elastomeric material, and exemplary outer coverings include various textiles having different stretchability properties. For example, the outer cover may be a strong and stretchable nylon outer cover providing resistance to extreme wear and tear, and affording strength and durability. The nylon outer cover may be used to increase radial stretch and comfortable elasticity.
In the prior art, liners may function to secure the residual limb within a prosthetic socket once the residual limb and sleeve are inserted into the socket in a close-fitting relationship by isolating the distal end area of the hard socket from atmosphere. Upon application of a pulling force on the liner relative to the socket, suction is created in the distal end of the socket tending to retain the liner within the socket. Appropriate devices are usually provided to enable expulsion of air between the distal end of the liner and the hard socket, and to isolate the distal end of the hard socket from atmosphere after the liner with the residual limb has been fully inserted within the socket.
In some applications, the liner is provided with an umbrella at its distal end and a threaded socket for receiving a securing pin member which then extends through an axial opening in the distal end of the hard socket for securing the hard socket relative to a prosthetic device mounted to the distal end of the socket. In other applications, the prosthetic device is secured to the exterior of the distal end of the hard socket and the sleeve member is fully contained within the hard socket.
In other applications, it may be desired to more positively secure the liner within the hard socket by creating a hypobaric (vacuum) pressure within the distal end of the hard socket between such distal end and the distal end of a liner inserted into the hard socket with a residual limb contained within the liner. The hypobaric pressure may be maintained at the distal end of the hard socket and the interior of the socket at its distal end will be isolated from atmosphere during normal retention of the liner within the hard socket. Opening the distal end of the socket to atmosphere releases the vacuum or hypobaric pressure within the socket to enable simple withdrawal of a residual limb with a liner thereon from the socket.
A pump or other device may be utilized to evacuate the distal end of the socket between the distal end of the liner and the distal end of the socket. A valve or other appropriate device typically is used to open and close the distal end of a socket to surrounding atmosphere.
Various arrangements are known for providing an appropriate seal between the exterior of the liner and the interior of the hard socket including external air impermeable sleeves covering the interface area between the proximal area of the hard socket and the adjacent liner body.
In trans-femoral applications, the sealing between a sleeve and a socket is generally simpler and easier to execute than sealing a trans-tibial liner against the inner surface of the socket because in the latter situation, the residual limb contains more bony protuberances and irregular shapes that are difficult to effectively seal, particularly if it is desired to simply use the material of the elastomeric liner as the sealing element.
Some users find that known liners having sealing means fail to sufficiently tolerate volume fluctuations, and may leave pressure marks on the residual limb after a period of sustained use. Additional improvements may be required for some users in that known liners do not adequately conform to the user's anatomy, and therefore fail to provide necessary comfort and skin protection. Moreover, as with all suspension liners having sealing means, it is necessary that the liner provides reliable suspension after an initial phase of volume and shape conditioning after the liner is donned on the user's residual limb.